The present invention relates generally to electrically powered mining equipment, and more particularly to the dissipation of the braking energy of electrically powered mining equipment by liquid-cooled braking resistors.
Vehicles used in the mining industry, such as mining haul trucks, electric shovels, and draglines, are often driven by high-powered electrical motors. In some applications, electrical power is supplied to the electrical motors from an external power station via a feed cable or trolley line. In other applications, electrical power is supplied to the electrical motors from a generator on board the vehicle; the generator can be driven, for example, by a diesel engine.
When an electrical motor is operating in the drive mode, it converts electrical energy into mechanical energy. When a moving vehicle slows down, however, the electrical motor operates in a reverse mode, converting mechanical energy into electrical energy. This electrical energy is typically dissipated as waste heat in braking resistors. The braking resistors, in turn, need to be cooled to avoid exceeding their service temperature.
In existing mining vehicles, the braking resistors are air cooled by fans. There are several disadvantages to air cooling. The overall assembly for the braking resistors occupies substantial volume: large braking resistors are needed to dissipate the required power; large spacings between braking resistors are needed to allow adequate air flow; and large, high-speed fans are needed to provide adequate cooling power. The volume of the assembly for the air-cooled braking resistors decreases the available cabin space for the operator of the vehicle and decreases the available payload for mining haul trucks. The fans, furthermore, generate high noise levels, which pose a potential safety hazard for the operator.